Electronically controlled fuel injector

Abstract

 The injector (10) for intermittently injecting fuel under high pressure in an internal combustion engine is provided with an injector valve member (18). The movement of this injector valve member (18) to open and close a fuel discharge orifice (24) is controlled by the fuel pressure in a control chamber (40) acting on a valve piston (26) on the side opposite to the discharge orifice (24). A cylindrical member (36) surrounds the upper part (30) of the valve piston (26). Energization of a solenoid (44) results in the opening of a pilot valve (46) and a subsequent quick drop of the fuel pressure in the control chamber (40). The solenoid (44) in addition to its function as a high speed actuator for the pilot valve (46) is also used to carry and transmit the force resulting from the fuel pressure in the control chamber (40) and acting on the cylindrical member (36), on the solenoid (44) and on further members (48, 50, 52, 14). Since the solenoid (44) can therefore be mounted directly within the injector housing (14), the design of the injector (10) can be very compact and simple.

Description

Technical Field

[0001] The present invention relates to an electronically controlled fuel injector for internal combustion engines as defined in the pre-characterizing clause of claim 1. Such a fuel injector is particularly suited for the direct injection at a high fuel pressure into the combustion chamber of the internal combustion engine.

Background and Summary of the Invention

[0002] Different designs of fuel injectors of this type with an electromagnetic control of the injector needle valve are known and disclosed in particular in EP-A-O 228 578 and also for example in the following publications: US-A-2,881,980, US-A-3,610,529 and US-A-4,566,416. These prior art injectors are bulky, either because of the lenght of the injector and/or because of the particular design of the members responsible for the electromagnetic control of the injector needle valve. If these known injectors are used in small internal combustion engines, such as passenger car engines, this bulkiness is a considerable drawback. In addition, the above mentioned, relatively complex injector designs are expensive to manufacture. This is also playing a very important role in an application for small engines.

[0003] It is now the object of the present invention to propose a fuel injector of the afore-mentioned type, which is of simple and compact design and which has definite space- and price advantages compared to the prior art solutions. An injector design is simple if the number and the dimensions of the single components are small and if the number of tight fits and accurately machined surfaces are minimized.

[0004] Furthermore the geometrical shape of the components must be so that the parts can be manufactured in a simple way.

[0005] According to the present invention this object is implemented by the features of the characterizing part of claim 1.

[0006] The advantage of the invention becomes apparent from the following detailed description of the embodiments shown in the drawings.

Brief Description of the Drawings

[0007] 

Fig. 1

is an axial sectional view of an electronically controlled fuel injector according to the present invention, and

Fig. 2

is a partial, axial sectional view of the particular solenoid and pilot valve design of the present invention.

Detailed Description of the Preferred Embodiments

[0008] Turning to Figure 1, a fuel injector of compact design in accordance with the present invention is designated by the numeral 10. This injector 10 is employed in a fuel injector system (not illustrated) for injecting pressurized fuel into the combustion chamber of an internal combustion engine.

[0009] The pressurized fuel supplied by a fuel pressure pump (not shown) enters the injector housing 14 through a passage 12 connected to a space or chamber 16 machined in the injector housing 14 which houses an injector needle 18. The injector needle valve 18 extends downwards to a valve seat 22 in a passage 20 of an injector tip 58. As shown in Figure 1 the injector needle valve 18 is engaged with the valve seat 22 and therefore blocks the passage of fuel from the injector 10 through injection orifices 24 into the combustion chamber of the related internal combustion engine (not illustrated).

[0010] The injection orifices 24 are machined into the injector tip 58. The tip 58 is engaged by a nut 56 and pressed onto a surface 14a of the injector housing 14 to prevent leakage of fuel from the space 16 to the outside of the injector 10.

[0011] In the upper portion, the injector needle valve 18 is provided with a needle valve piston 26 with two sections 28 and 30 of different outer diameters. The section 28 with the smaller outer diameter is slidably guided in a tight-fitted manner in a guide-bore 28a of the injector housing 14. The tight fit between guide-bore 28a and the section 28 of the needle valve piston 26 greatly reduces fuel leakage from the high pressure section 16 of the injector 10 into an upper neighbouring low pressure region 42.

[0012] The needle valve piston 26 is firmly connected to the injector needle valve 18, either because the valve piston 26 is made of one piece with the injector needle valve 18 or by pressfitting or welding the parts together as shown in Fig. 1. In the inside of the needle valve piston 26 is provided a bore 32 which is connected at one end by means of a side bore 33 to the space 16 of the injector 10. On the other end bore 32 connects to a much smaller bore or orifice 34. The orifice 34 extends to the top end surface of the section 30 of the needle valve piston 26. The section 30 is guiding on its outer diamter a piece 36 by means of a tight slide-fit guide 30a. The piece 36 is closed at the upper end which is provided with an orifice 38. Internally the piece 36 defines, together with the section 30 of the needle valve piston 26, a small space or chamber 40. Both orifices 34 and 38 are axially aligned and extend in the direction of the longidudinal axis 8 of the injector 10.

[0013] A pilot or solenoid valve 46 comprises a valve stem 60 made of hard material and a valve plate 62 made of a soft electromagnetic material and firmly connected with the valve stem 60. As shown in Figure 1, the pilot valve 46 which can be actuated by means of a solenoid 44, is closing the outlet of the orifice 38, thus preventing fuel from flowing through the orifice 38 into the neighbouring low pressure region 42. The cylindrical piece 36, due to the force resulting from the fuel pressure in the small chamber 40, will be pressed against a plane contacting surface 48a of a member 48. The member 48, together with further elements mounted within the injector 10, determines the axial position of the cylindrical piece 36, in a manner not explained in detail.

[0014] A guide piece 50 is transmitting to the solenoid 44 by means of contacting surfaces 50a and 44a the axial hydraulic force which is transmitted from the cylindrical piece 36 to the member 48. This axial force resulting from the fuel pressure in the small chamber 40 will be transmitted from the solenoid 44 to the solenoid retaining nut 52 by means of the contacting surface 52a. Finally, the axial force is transmitted by a thread 54a of the solenoid retaining nut to the corresponding thread 54b provided at the injector housing 14. The path of the axial force resulting from the fuel pressure will be closed by a nut 56, a tip 58 and the injector needle valve 18.

[0015] The solenoid 44, like the plate 62, is made of soft electromagnetic material. The electromagnetic properties (magnetisation and dynamic response) are adversely affected by mechanical tensions (material stresses) . This fact would negatively influence the behaviour of the solenoid 44 and therefore of the solenoid valve 46 if the solenoid 44 would be used to carry the axial force resulting from the fuel pressure in the small chamber 40 without taking preventive measures.

[0016] The reason why the solenoid 44 can be used as force transmitting element without impairing the proper function thereof will become apparent during the description of Figure 2, where the design of the solenoid 44 is explained in detail.

[0017] However, even from Figure 1, one recognizes that the contacting surfaces 44a and 52a are arranged at a radial distance from the longitudinal axis 8 which is fairly bigger than the radius of the solenoid valve plate 62. This fact together with the internal layout of the solenoid 44 according to the present invention enables the solenoid 44 to perform both the task of a fast responding device and of a carrying member of the axial force resulting from the fuel pressure in the small chamber 40.

[0018] In the injector design according to EP-A-0 228 578 it is necessary to place the solenoid in an additional housing This housing is used to carry the axial hydraulic force resulting from the fuel pressure and to prevent mechanical loads from disturbing the correct function of the solenoid. However, this housing results in increased dimensions of the injector as well as in additionally needed components compared to the design according to the present invention.

[0019] The solenoid 44 and the guide-piece 50 of the present invention are placed directly and without additional housing in a bore 64 of the injector housing 14, which allows to achieve a much more simple and compact design.

[0020] In a cross bore 66 of the injector housing 14 and of the guide-piece 50 there is located a pilot valve spring 68 which is constructed as a bending spring in the shape of a round bendable bar extending through a bore 70 machined in the stem 60 of pilot valve 46 and transmitting its elastic bias force onto the under side of said bore 70. The pretensioning force of the pilot valve spring 68 can be set by moving both ends of the spring 68 by means of two slotted pins 72. Each one of the pins 72 is guided in a bore 72a of the injector housing 14. An adjusting nut 74 threaded on the lower portion of the thread 54b of the injector housing 14 is used to determine the axial position of the two pins 72 and therefore serves to determine the spring bias force to the pilot valve stem 60. This pretensioning operation can be performed once the injector 10 is fully assembled.

[0021] The adjusting nut 74 and the solenoid retaining nut 52 are provided with slotted sleeves 76a and 76b. The slotted sleeve 76b of the adjusting nut 74 is provided with a thread at its inner surface which corresponds to the thread of the adjusting nut 74. The solenoid retaining nut 52 and the adjusting nut 74 can be blocked by means of a clamp 78 and elastic deformation and pressing of the slotted sleeves 76a and 76b against each other and against the thread 54b of the injector housing 14. Thus an undesired rotation of the nuts 52 and 74 of the injector can be prevented.

[0022] Furthermore the injector 10 is provided with a side-cover 80 which can be removed to install or remove the pilot valve spring 68 as well as with a pin 81 to prevent the rotation of the guide piece 50. Three O-rings 82a, 82b and 84 seal the low pressure region 42 of the injector 10. A fuel return piece 88 allows fuel under low pressure to be returned from the low pressure region 42 back to the fuel tank (not shown). Two plugs 86a and 86b which are the terminals of the coil of the solenoid 44 serve as connectors for connection to the solenoid driver unit (not shown).

[0023] The mode of operation of the injector 10 is the following:
When at a desired point of time the solenoid 44 is energized by an electric pulse of a predetermined duration, the pilot valve 46 is operated and the pilot valve stem 60 is retracted from the seat, thus opening the outlet of the orifice 38. In the same way as explained in the afore-mentioned EP-A 0 228 578 the fuel pressure in the small chamber 40 drops abruptly. The fuel pressure acting on the lower side of the lower section 28 of the injector needle valve piston 26 can now shift the needle valve 18 in its opened position and the injection event begins by the discharge of fuel across the seat 22 and through the injection orifices 24.

[0024] If the electric pulse to the solenoid 44 is interrupted, the pilot valve 46 is quickly shifted back to its seat at the outlet of the orifice 38 by means of the biasing spring 68. The pressure in the small chamber 40 will abruptly rise and the injection event will be terminated.

[0025] In place of the clamp 78 and the nut 74 a countering nut and a washer can be provided in the embodiment of Figure 1 to block a modified solenoid retaining nut 52.

[0026] The members 48, 50, 52 and the solenoid 44 are used to carry the axial force resulting from the fuel pressure in the small chamber 40 and to transmit this force back to the injector housing 14. Care must be taken that the contacting surfaces 48a, 50a, 44a and 52a do not bring about lateral forces that are transmitted to the guide 30a of the upper piston of the injector needle valve 18. If one or more of the surfaces 48a, 50a, 44a and 52a are not perpendicular to the injector's longitudinal axis 8, or if the guide 28a for the lower section of the needle valve piston 26 is not aligned with the bore 64, undesired high frictional forces at the guides 28a and 30a can hinder a reliable and repeatable operation of the injector needle valve 18. This problem can be solved by making at least one of the contacting surfaces 44a or 52a slightly spherical in such a way that a slight non-perpendicularity can be compensated. For example the contacting surface 52a between the solenoid 44 and the solenoid retaining nut 52 could be slightly spherical.

[0027] Figure 2 shows in detail the design of the solenoid 44. The solenoid 44 consists of a round body 122 and of a stator plate 124. The stator plate 124 is fitted in a bore 124a in an outer section 126 of the body 122 which is radially and axially determining the position of the stator plate 124 by means of its bore 124a and of a shoulder 128. A coil 130 is wound on a coil body 132 of plastic and is placed in the ring-shaped space delimited by the inside of the body 122 and by the inside surface of the stator plate 124. The two electrical connections 86a and 86b of the coil 130 protrude out of the two bores 134a and 134b on the back side of the body 122. An inner round section 138 of the solenoid body 122 protrudes through a central bore 136 of the stator plate 124. An O-ring 140 seals the ring-shaped space housing the coil 130 from fuel present in the region 142. The region 142 is connected through a bore 144 and by other passages of big cross sectional area compared to the cross sectional area of the two orifices 34 and 38 with the low pressure region 42 (see also Figure 1).

[0028] The side of the stator plate 124 facing the region 142 and the pilot valve plate 62 is in its essence flat and lies in the same plane as the front surface of the inner round section 138 of the solenoid body 122. The outer diameter of the pilot valve plate 62 is substantially smaller than the diameter of the circumference 146 of the solenoid body 122. Two pole faces 150 and 148 are defined between the surface of the inner round section 138 and the inner portion of the pilot valve plate 62 (first pole face 150) as well as between the outer portion of the pilot valve plate 62 and the inner portion of the stator plate 124 (second pole face 148). The two pole faces 148 and 150 are ringshaped and have a substantially equal surface area. In comparison to the surface area of every single of the two pole faces 148 or 150, the cross sectional area of the outer section 126 of the solenoid body 122 and of the outer border of the stator plate 124 are substantially bigger.

[0029] To enable a very rapid movement of the pilot valve 46 immediately after the switching-on and switching-off of the electrical power to the coil 130, the pilot valve 46 and therefore the pilot valve plate 62 must have a very small mass and at the same time the electromagnetic material of the pole faces 148 and 150 must be saturated in order to obtain the biggest possible electromagnetic force with the smallest possible mass of the pilot valve plate 62. The proposed design produces a concentration of the electromagnetic flux at the pole faces 148 and 150 as well as in the sections of the electromagnetic loop which are free from mechanical stresses. These sections are: The pilot valve plate 62, the inner round section 138 of the solenoid body 122 and the inner portion of the stator plate 124.

[0030] Because the maximum concentration of the electromagnetic flux is reached at the pole faces 148 and 150, because the total flux is constant in any cross section of the electromagnetic loop and because the cross sectional areas of the outer section 126 of the solenoid body 122 and of the outer border of the stator plate 124 are substantially bigger compared to the surface of one pole face 148 or 150, the flux concentration in these portions of the electromagnetic loop will be much weaker. Due to this fact mechanical stresses in the outer section 126 do not influence the performance of the solenoid 44. Therefore, the outer section 126 of the solenoid body 122 can be used to carry and transmit the force arising from the pressure in the small chamber 40 (see Figure 1) in addition to its function in the electromagnetic loop, and thus a very simple design of the injector 10 according to the present invention can be realized.

Claims

1. Fuel injector for intermittently injecting fuel into the combustion chamber of an internal combustion engine, comprising a housing (14) with a valve seat (22) and at least one injection orifice (24), an elongated injector valve member (18) provided with a piston member (26) and mounted within said housing (14) for engagement with said valve seat (22) to close said injection orifice (24), said injector valve member (18) being shiftable in its axial direction to be momentarily lifted from said valve seat (22) to open said injection orifice (24) to allow the injection of a desired quantity of fuel into the combustion chamber of the internal combustion engine, a control chamber (40) provided within said housing (14) and being connected to a fuel supply line (12); the fuel pressure in said control chamber (40) acting upon said piston member (26) of said injector valve member (18) forcing the latter against said valve seat (22), means (34, 38, 44, 46) to quickly reduce and quickly restore the fuel pressure in said control chamber (40) to allow the axial movement of said injector valve member (18), said means to quickly reduce and restore the fuel pressure in said control chamber (40) comprising at least a discharge orifice (38) opening into said control chamber (40) and electromagnetically controlled pilot valve means (46) for closing and temporarily opening the outlet side of said discharge orifice (38) and operated by a solenoid (44) depending upon applied electric pulses of a predetermined duration; at least one first member (36) defining in part said control chamber (40) and being subject at least to the fuel pressure present in said control chamber (40), said first member (36) being in mechanical connection with further members (48, 50, 52, 54, 14) transmitting the hydraulic forces acting upon said first member (36) characterised in that the solenoid (44) comprises a body (122) having an outer section (126) and an inner section (138), and a solenoid coil (130) which is placed in an inner space of said body (122) between said outer and inner sections (126, 138); and that said further members include the outer section (126) of said body (122) of the solenoid (44), whereby said solenoid (44) in addition to its function as an actuating device for said pilot valve means (46) is also used to carry and to transmit said forces from one of said further members (50) to a next one of said further members (52).

2. Fuel injector according to claim 1, wherein said solenoid body (122) defines a pole face (148, 150) facing an armature member (62) connected to the stem (60) of said pilot valve means (62).

3. Fuel injector according to claim 1, wherein said further members (48, 50, 52, 14) comprise a guide piece (50) to carry and transmit said forces from said first member (36), said guide piece (50) being located in a bore (64) provided in said injector housing (14) and being radially guided therein; said guide piece (50) radially guiding said pilot valve means (46) and being in connection with said outer section (126) of said solenoid body (122) for transmitting said forces resulting from the fuel pressure within said control chamber (40) to said solenoid body (122) which is in connection with a solenoid retaining member (52) which is connected to said injector housing (14) and therewith transmits said forces from said solenoid body (122) to said injector housing (14).

4. Fuel injector according to claim 1, wherein said solenoid (44) is radially guided within a bore (64) provided in said injector housing (14).

5. Fuel injector according to claim 1, comprising a pilot valve spring (68) constructed as a bendable bar, both ends of which are pretensioned to a desired value, said bendable bar (68) engaging said pilot valve means (46) intermediate its ends.

6. Fuel injector according to claim 5, comprising biasing means (72, 74) displaceable in the direction of the longitudinal axis (8) of said injector (10) and acting upon both ends of said pilot valve spring (68) whereby axial displacement of said biasing means (72, 74) brings about a change of the bias force exerted by said pilot valve spring (68) upon said pilot valve means (46).

7. Fuel injector according to claim 6, wherein said biasing means (72, 74) comprise two pins (72) and a nut (74), each pin (72) being received in a bore (72a) provided in the injector housing (14), one end of each pin (72) protruding out of said bore (72a) and contacting said nut (74) and the other end of each pin (72) acting upon one end of said pilot valve spring (68), said nut (74) being provided with an internal thread engaging an external thread (54b) of the injector housing (14) whereby a rotation of the nut (74) results in an equal axial displacement of both pins (72).

Drawing